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California and the Fourth Amendment

On Wednesday, the United States Court of Appeals for the Ninth Circuit is scheduled to reconsider whether California violates the Fourth Amendment’s prohibition against searches and seizures by requiring police to take DNA samples from people arrested but not yet convicted of felonies. California’s law is ostensibly aimed at accurately identifying those arrested, solving crimes and exonerating the innocent. It is also, unfortunately, unconstitutional.

An appeals court panel ruled otherwise in February. In a 2-to-1 vote, it said the law was reasonable, a view with prominent support. In July, Chief Justice John Roberts Jr. wrote that there was “a reasonable probability” that the Supreme Court would address the issue this term in a Maryland case and that there was “a fair prospect” that it would rule as the appeals court panel had in the California case. This is a matter of national import because the federal government and more than half the states have laws allowing DNA sampling before conviction.

The constitutional outcome should be clear. Unless there is a warrant, or suspicion of a different crime that a DNA sample would help solve, taking a sample violates established rights against unreasonable search and seizure under the Fourth Amendment. The harms to individuals — invasions of their privacy, the risks of false positives in DNA matches — outweigh the modest benefits to law enforcement. Of the 300,000 or so people arrested in California each year for felonies, about a third are never convicted and many are never charged.

The disagreement in the three-judge panel turns on clashing views about the law’s purposes for requiring DNA samples. The law says the primary purpose is identification. The majority enlarged that definition, asserting that the law’s purpose is to identify suspects and to help investigate other crimes. But since people arrested are identified by their fingerprints, the dissent was surely correct that the law’s real purpose was investigation: “The DNA is taken because there is a possibility that the DNA may help solve some other crime.” When the state takes a DNA sample, it creates a DNA profile and enters that into the system of federal, state and local DNA databases used in investigations. Known as Codis, the system links DNA traces from crime scenes to individuals — connecting them, sometimes falsely, to alleged criminal activity.

Taking samples from people arrested apparently results in a handful of cases being solved more quickly, but that benefit is small. It does not justify the substantial harm from taking DNA without probable cause from tens of thousands of innocent people in California each year.

A version of this editorial appears in print on September 19, 2012, on Page A28 of the New York edition with the headline: California and the Fourth Amendment. Today's Paper|Subscribe